Use following address in your browser: https://xxx.xxx.xxx.xxx/httpapi.asp?command=getStatusEx (ignore any SSL/TLS warnings)
Just change xxx.xxx.xxx.xxx to IP address of your device, you can find it in WiiM Home app.
New firmware (5.0.540148) changed the power consumption in stand-by mode, it's now about 3.8W, device is no longer warm in this mode. Unfortunately, buzzing noise is still there.